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Basic OverviewECG Rhythm Interpretation
Objectives
To recognize the normal rhythm of the heart - “Normal Sinus Rhythm.”
To recognize the most common rhythm disturbances.
To identify emergency interventions for life threatening arrhythmias
I. Impulse Conduction & the ECG
Sinoatrial node
AV node
Bundle of His
Bundle Branches
Purkinje fibers
1. The “PQRST”-Reminder-the EKG only reflects the Reminder-the EKG only reflects the heart’s electrical activity-heart’s electrical activity-not its not its contractioncontraction P wave - Atrial
depolarization
• T wave - Ventricular repolarization
• QRS - Ventricular depolarization
2. The PR Interval
Atrial depolarization +
delay in AV junction
(AV node/Bundle of His)
(delay allows time for the atria to contract before the ventricles contract) normal time 0.12 to 0.20 sec.
3. Pacemakers of the Heart
SA Node - Dominant pacemaker with an intrinsic rate of 60 - 100 beats/minute.
AV Node - Back-up pacemaker with an intrinsic rate of 40 - 60 beats/minute.
Ventricular cells - Back-up pacemaker with an intrinsic rate of 20 - 40 beats/minute.
4. The ECG Paper Horizontally
One small box - 0.04 sOne large box - 0.20 s
VerticallyOne large box - 0.5 mV
4. The ECG Paper (cont)
Every 3 seconds (15 large boxes) is marked by a vertical line (hash mark).
This helps when calculating the heart rate. You need a 6 second strip to calculate
heart rate (30 large boxes)
3 sec 3 sec
4. The ECG Paper (cont)
Count the number of P waves in a 6 second strip (30 large boxes) and multiply by 10 to determine atrial rate (9 x 10 = 90) Atrial rate = 90 beats/min
Count the number of QRS complexes in a 6 second strip (30 large boxes) and multiply by 10 to determine ventricular rate (9 x 10 =90) Ventricular rate + 90 beats/min
3 sec 3 sec
II. Normal Sinus Rhythm (NSR)Normal Rhythm of Heart--etiology
Etiology: the electrical impulse is formed in the SA node and conducted normally.
This is the normal rhythm of the heart; other rhythms that do not conduct via the typical pathway are called arrhythmias.
II. Normal Sinus Rhythm (NSR)Characteristics
Rate – 60 to 100 Regularity – rhythm is regular P waves – one P wave preceding each QRS PR interval – normal between 0.12 and 0.20 seconds and
constant in length QRS – all look the same QRS duration – equal to or less than 0.12 seconds and
constant in width QT interval – equal to or less than 0.44 seconds and constant in
length
III. SA Node Problemsdefined
The SA Node can: fire too slow fire too fast
Sinus Bradycardia
Sinus Tachycardia
A. Sinus BradycardiaRate less than 60 beats per minute--etiology
Etiology: SA node is depolarizing slower than normal, impulse is conducted normally (i.e. normal PR and QRS interval).
Significance: Lower rate may cause decrease in cardiac output
A. Sinus Bradycardia--
Characteristics
Rate: less than 60 beats per minute Regularity: rhythm is regular P wave: normal; one precedes each QRS PR interval: normal between 0.12 and 0.20
seconds QRS: normal, equal to or less than 0.12 seconds QT: normal or may be prolonged
A. Sinus BradycardiaSigns and Symptoms due to Sinus Bradycardia
May have no symptoms at all May have signs of decreased cardiac output - hypotension, cool clammy skin, - shortness of breath, chest pain or pressure - light headed, dizziness or blurred vision - syncope
A. Sinus BradycardiaTreatment for Sinus Bradycardia
Treat only if symptomatic - IV atropine
- IV dopamine
- Transcutaneous pacemaker
B. Sinus Tachycardia--etiologyRate greater than 100 beats per minute but less than 150 beats per minute
Etiology: SA node is depolarizing faster than normal, impulse is conducted normally.
Significance: increased workload of the heart Remember: sinus tachycardia is a response to
physical or psychological stress, (hypoxia, pain, hypovolemia).
B. Sinus Tachycardia-characteristicsRate greater than 100 beats per minute but less than 150 beats per minute
Rate: 100 beats per minute but less than 150 beats per minute.
Regularity: rhythm is regular P wave: normal, one precedes each QRS PR interval: normal between 0.12 and 0.20
seconds QRS: normal, equal to or less than 0.12 seconds QT: normal
B. Sinus TachycardiaSigns and Symptoms
May have no symptoms at all May have signs of decreased cardiac output
- hypotension, syncope and blurred vision
- chest pain and/or palpitations
- may report a sense of nervousness or anxiety
B. Sinus TachycardiaTreatment
Look for the cause (ie. pain, anxiety, fever, hemorrhage) and treat the cause.
If tachycardia leads to cardiac ischemia treatment may include medications to slow the heart rate Beta blockers or Calcium channel blockers
III. Atrial Arrhythmias
Single or Multiple irritable areas can depolarize and “take over” from the SA node.
Atrial tissue
A. Atrial Fibrillation etiology
Etiology: Atrial impulses are formed in a totally unpredictable fashion-there are no p waves.
Significance: The atria do not contract in a coordinated way
therefore, the cardiac output is decreased. The atria do not empty fully, so there is a risk of
atrial clots The AV node allows some of the impulses to pass
through at variable intervals (so rhythm is irregularly irregular). Rates can get dangerously high
A. Atrial Fibrillation characteristics
Rate:
Atrial rate: not measurable exceeds 400 beats per minute.
Ventricular rate: 30 to 220 beats per minute
Regularity: grossly irregular
P waves: absent; erratic baseline
PR interval: not measurable
QRS: normal QT: not measurable
A. Atrial Fibrillation Signs and symptoms
Patients with chronic atrial fibrillation may be asymptomatic
New onset atrial fibrillation patients may have symptoms related to decreased cardiac output (loss of atrial contraction and fast ventricular rate)
•hypotension, cool clammy skin,
•shortness of breath, chest pressure or pain,
•dizziness, blurred vision or syncope
A. Atrial Fibrillation treatment
If treatment is required:
Beta Blocker, Calcium Channel blockers will decrease rate
IV Amiodarone may decrease rate and convert rhythm (NOT IV bolus!)
Synchronized Cardioversion will convert the rhythm
B. Atrial Flutter
Deviation from NSRNo P waves. Instead flutter waves (note
“sawtooth” pattern) are formed at a rate of 250 - 350 per minute
Only some impulses conduct through the AV node
Significance & treatment -as in Atrial Fibrillation
C. Supra Ventricular Tachycardia (SVT)Atrial Tachycardia
Deviation from NSR Heart rate: speeds up to greater than 150 beats per
minute Rhythm: regular, with normal QRS complexes.
Significance: Greatly increased myocardial oxygen demand Could become life threatening
C. SVT – Signs and symptoms
Patient may be asymptomatic
May have signs of decreased cardiac output:
•Hypotension, cool clammy skin,
•shortness of breath, chest pain or pressure,
•dizziness, blurred vision or syncope
C. SVT Treatment
Treatment:
1. Adenosine followed by Beta Blocker or Calcium Channel Blocker
2. Synchronized Cardioversion in emergency
IV. Ventricular Cell ProblemsVentricular cells can: fire occasionally from
1 or more irritable area
fire continuously from multiple irritable areas
fire continuously from a single irritable area
Premature Ventricular Contractions (PVCs)
Ventricular Fibrillation
Ventricular Tachycardia
(VT)
IV. Ventricular beatsWhen an impulse originates in a ventricle:
conduction through the ventricles will be abnormal
QRS will be wide (greater than 0.12 seconds) and bizarre.
Multi-focal PVCs
IV. Ventricular Conduction
NormalSignal moves rapidly through the ventricles
AbnormalSignal moves slowly through the ventricles result is a wide QRS
A. PVCs--characteristics
Deviation from NSREarly beats originate in the ventricles
resulting in wide (greater than 0.12 sec.) and bizarre QRS complexes.
When there is more than one premature beat, and the beats look alike, they are called “unifocal”.
When there is more than one premature beat, and the beats look different, they are called “multifocal”.
A. PVCs etiology
Etiology: Ventricular irritability can be caused by hypoxia, electrolyte imbalances.
Significance: Early beats from the ventricle do not deliver full cardiac output; if untreated may lead to VT/VF.
B. Ventricular Tachycardia
Deviation from NSR:Impulse is originating in the ventricles (no P
waves, wide QRS, rate greater than 100).
Significance: greatly reduced cardiac output--Life threatening
arrhythmia!! Treatment:
IV Lidocaine or IV Amiodarone (NOT IV bolus)
C. Ventricular Fibrillation
Etiology: Hundreds of ventricular cells are excitable and depolarizing randomly
Significance: no cardiac output; no pulse Death producing arrhythmiaDeath producing arrhythmia
Treatment: CODE BLUE1. Defibrillation2. IV Epinephrine3. IV Amiodarone
V. Heart Blocks(Bradycardia)
Etiology: weakness, fatigue or damage to the AV node
Significance: Bradycardia may result in decreased cardiac output
Treatment (same as for bradycardia): IV Atropine IV Dopamine Transcutaneous Pacing
A. 1st Degree AV Block
Etiology: Prolonged conduction delay in the AV node or Bundle of His.
PR interval: greater than 0.20 seconds and is constant
B. 2nd Degree AV Block, Type I
Etiology: Each successive atrial impulse encounters a longer and longer delay in the AV node until one impulse (usually the 3rd or 4th) fails to make it through the AV node.
P waves: More than QRSs P-R interval: gets progressively longer
C. 2nd Degree AV Block, Type II
Etiology: Conduction is all or nothing (no prolongation of PR interval); typically block occurs in the Bundle of His.
More P waves than QRSs PR interval does not vary in length
D. 3rd Degree AV Block
Etiology: There is complete block of conduction in the AV node; atria and ventricles form impulses independently of each other.
More P: waves than QRSs QRS to QRS (ventricular rate) is regular P to P (atrial rate) is regular—faster than
ventricular rate
3rd Degree AV BlockCharacteristics
40 bpm• Rate?• Regularity? regular
no relation to QRS
wide (greater than 0.12 s)
• P waves?
• PR interval? none• QRS duration?
SummaryRhythm Rate (beats per
minute)Regularity Comments Treatment
Sinus 60-100 Regular Normal rhythm of heart None
Sinus Bradycardia Less than 60 Regular Slow rhythm-can cause symptoms of decreased cardiac output
If symptomatic: atropine 0.5 mg IV push
Sinus Tachycardia 100 – 150 Regular Fast rhythm-caused by fever, pain, dehydration
Treat the cause
Suprventricular Tachycardia (SVT)
Greater than 150 Regular Fast-can cause symptoms of decreased cardiac output
Adenosine, -blockers, Diltiazem (Cardizem), Cardioversion if unstable
Atrial Fibrillation 350-400 Irregular No p-waves, PR not measurable -blockers, Diltiazem (Cardizem)
Atrial Flutter 250-350 Regular or Irregular
No p-waves, flutter waves—sawtooth pattern
-blockers, Diltiazem (Cardizem)
Premature Ventricular Contractions
Varies—can be normal
Irregular Early beats, wide, bizarre Amiodarone
Ventricular Tachycardia
100-250 Regular Wide, regular, fast; no p-waves Amiodarone—if pulseDefibrillation—if pulseless
Ventricular Fibrillation
Rapid, Chaotic No pattern; Can lead to death Defibrillation!
End of Reading
Summary—Heart BlocksName of Block # p-waves
compared to # QRS complexes
PR interval QRS complexes
Treatment
First degree # p-waves = # QRS complexes
PR interval longer than 0.20; constant
All present Atropine, if slow
Second degree type I
More p-waves than QRS complexes
PR interval gets longer and longer
QRS dropped periodically
Atropine, if slow
Second degree type II
More p-waves than QRS complexes
PR interval is constant
QRS dropped periodically
Transcutaneous pacing
Third degree Complete block
More p-waves than QRS complexes
No PR interval; P to P constant
QRS to QRS constant
Transcutaneous pacing
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